Abstract
The labeling of AS1411, a guanine (G)‐rich oligonucleotide (ON), conjugated with [^18^F]SFB was evaluated at different experimental conditions: ON concentration, base composition (G‐rich [AS1411] vs cytosine‐rich [CRO]), ON purity (desalted vs high‐pressure liquid chromatography (HPLC)‐purified) and buffers (tris‐HCl, sodium borate, and potassium phosphate (PBK)). The labeling yield, defined as % F‐18 incorporated into the ON, of HPLC‐purified AS1411 was significantly improved with increasing concentration – 7±3, 12±2, and 25±5% (n=5) at 56, 93, and 160 nmol/100 µL, respectively. The labeling yields, however, were much higher if guanines of AS1411 were completely replaced by cytosines – 22±1, 41±2, and 59±3% (n=3), respectively, at the same corresponding concentration (p<0.05). The specific activity of ^18^F‐AS1411 and ^18^F‐CRO was 4.2–12.6 and 4.2–25 mCi/µmol, respectively, after alcohol precipitation. If desalted grade of AS1411 and CRO was used instead for the conjugation, the yields were dropped to only 0–5 and 0–1 (n=5), respectively, regardless of the concentration used. The labeling yields were 5±2, 12±3, and 31±4 (n=3) at 200 nmol/100 µL of AS1411; and 30±2, 45±3, and 68±4 (n=3) at 200 nmol/100 µL of CRO for tris‐buffer, sodium borate, and PBK, respectively, at pH of 8.5 (p<0.05). Copyright © 2007 John Wiley & Sons, Ltd.